1. Field of the Invention
This invention relates to a clamping apparatus for an injection molding machine and, especially, to a clamping apparatus provided on a movable platen which is moved reciprocally, along tie rods, by a die opening and closing device.
2. Description of the Prior Art
As disclosed in Kokai (Jpn. unexamined patent publication) No. 8-174613, there is a known injection molding machine in which a movable platen is moved reciprocally, along tie rods, by a die opening and closing device provided on a stationary platen. A clamping apparatus is provided on the movable platen. In the prior art, the movable platen and a clamping drive member (cylinder device) are located on the same base so as to prevent the movable platen and the clamping drive member from moving independently during the opening and closing of the die and the clamping operation.
However, in the prior art, even though the movable platen and the clamping drive member are located on the same base, they do not necessarily move together synchronously and a deviation of the center positions thereof or an inclination thereof can often occur because the movable platen and the clamping drive member are moved along the tie rods and due to inertia.
Further, in the prior art, there is a problem that, when the thickness of the die is changed, an adjustment of the distance between the clamping drive member and the movable platen is complicated and it is necessary to adjust the distance therebetween on the base.
In view of the above-mentioned problem, the present invention is aimed at provision of a structure of a clamping apparatus for an injection molding machine in which no deviation of the center positions of the movable platen and the clamping drive member or no inclination of the both occurs and the distance therebetween can be easily adjusted and held.
Namely, in the invention claimed in Claim 1, there is provided a clamping apparatus for an injection molding machine, in which a movable platen is moved reciprocally, along tie rods, by a die opening and closing device, said movable platen being provided with a clamping apparatus for clamping, a driving plate provided with a securing device for securing the tie rods in a predetermined position in the axial direction, and a clamping drive device for pressing the movable platen, said driving plate being guided by guide bars, secured to said movable platen, in the axial direction, rear parts of said guide bars being secured to an adjusting plate which is provided with a positioning means for adjusting and holding a distance between said driving plate and said movable platen.
The invention claimed in Claim 2 provides a clamping apparatus for an injection molding machine as set forth in Claim 1, wherein said positioning means comprises a ball-screw provided on said driving plate, a ball nut provided on said adjusting plate and engageable with said ball-screw, and a servomotor for rotating said ball-screw.
In the invention claimed in Claim 3 or 4, a plurality of clamping drive devices are provided for a pressing surface of said movable platen.
According to the invention claimed in Claim 5, a clamping apparatus for an injection molding machine further comprises an ejector device having an ejector plate provided with ejector pins projecting therefrom and guided by said guide bars in the axial direction.